Ever wonder what those little blue particles are in some toothpastes? One of our scientists did, and started to investigate their effects on teeth brushing. Known as microbeads or microplastics, these blue particles are usually polyethylene or polypropylene. They are commonly included as exfoliants in face cleansers, and may be added to toothpaste for visual effects.
CPG researcher Lucas Rossier performed a bench top study comparing enamel wear using toothpastes with and without microbeads. A model enamel substrate was used in place of an actual tooth surface. Through optical and electron microscopy, Rossier showed greater scratching and abrasive wear in the toothpaste containing microbeads. Although the results may not be directly comparable to actual tooth enamel wear, they do demonstrate that the microparticles have an abrasive effect that is greater than the toothpaste alone.
Okay, so my wife may disagree. However, the long chain nature of a lot of food products (i.e. their polymeric nature) allows us to at least understand the physics behind the behavior of food.
Cooks have known the secret of thickening sauces and gravies with a fairly small amount of flour or cornstarch. A key aspect of this process is to add the flour or starch when the sauce is fairly cool, mix well, and THEN apply heat. At some point in the heating process, the sauce will magically start thickening (i.e. the viscosity increases).
So what is happening? First off, the key material is starch, which is found in flour and of course corn starch. Starch is a polysaccharide, or a polymer made up of glucose (sugar) repeat units with glycosidic bonds. Starch is derived from various types of plants, and can have varying degrees of amylose and amylopectin, the two types of molecules making up starch. At room temperature, starch is not soluble in water, due to its crystalline nature. The molecules in the starch can fold themselves into tightly ordered sections, with thousands of the amylose and amylopectin molecules tightly bound into small micron-sized particles. This is how they initially start in the sauce. The small particles do not affect the viscosity in any measurable way. Once the sauce is heated, however, sufficient energy is put in the starch granules to overcome the melting point, and the chains start to unfold, stretching out and entangling with other chains. The long, entangle molecules of the amylose and amylopectin increase the viscosity of the sauce, thereby ‘thickening’ it.
Having problems with lumps in your gravy? The gravy was too warm when you added the flour or corn starch, and the starch granules began to swell and expand while they were still in a bundle, preventing them from spreading out in the gravy. By adding them to cool gravy, you can distribute the granules before they expand and entangle.
This thickening behavior of gravy with temperature can be nicely captured by shear rheometry.
A common science experiment is to have a student place a rubber band against their lips while rapidly stretching the rubber band. The student will feel the rubber band heat up. Rapidly relaxing the rubber band will result in the band cooling. What is happening is that in an unstretched state, the rubber molecules are randomly organized; stretching the rubber band orients the molecules, thereby reducing their entropy (state of randomness). If this is done quickly, the rubber band heats up as the heat generated internally by this decrease in entropy cannot be dissipated rapidly enough to the surrounding atmosphere. Likewise, when the entropy is rapidly increased by relaxing the rubber band, energy is consumed by the rubber band, resulting in its cooling.
This effect has been termed the elastocaloric effect, and is being investigated as a means of providing cooling as an alternative to the typical vapor compression cycle used in most refrigerator and air conditioner units. This change in molecular level ordering can be accomplished through mechanical means, magnetic means, or electrical means (the latter two termed magnetocaloric or electrocaloric cooling). A key technological challenge is identifying materials that can handle the millions of cycles of fatigue behavior without change.
The Department of Energy is exploring these alternative technologies as part of their interest in greener building technologies. The key metric for success is an improved coefficient of performance (COP) of the new technologies (ratio of the delivered cooling energy to the total input wattage of the device) vs. existing vapor compression cycles, which are around 3-4.
This time of year, our thoughts turn to tryptophan, a chemical associated with the perceived sleep-induced nature of turkey. Tryptophan is an essential amino acid (see the NH2 and COOH above), meaning that we do not naturally produce this compound, but that it is a necessary part of our diet in order for protein synthesis to occur. Tryptophan is found in many protein-based food products, including oats, chocolate, red meats, milk products, and many seeds and nuts. While tryptophan is found in turkey, the quantities are no more than what you find in chicken or other fowl. For example, 100 grams of turkey has 0.24 grams of tryptophan, the same as chicken, while cod has 0.7 grams, and an egg white has 1.0 grams. It is true, however, that tryptophan can cause drowsiness, so monitor your protein intake prior to driving.
Tryptophan and other amino acids are normally analyzed with HPLC. However, GC-MS can be used on more volatile amino acids, which provides more identification capabilities than offered by HPLC. The polar nature of tryptophan requires that the amino acid is derivatized prior to GC-MS analysis, however, which increases the volatility of the compound, a necessary property for GC-MS. Often times, silylation is performed to derivatize the amino acid. In this process, a silicon-alkyl compound reacts with the hydroxyl group, creating an Si-O bond where the hydroxyl group used to be. This reaction results in a volatile, and more stable, compound for GC-MS analysis. Identification and quantification can now occur.
Fatigue crack propagation testing provides users information about the resistance of a material to crack initiation and propagation under cyclical loading. Currently, ASTM E647 is used to monitor the crack propagation behavior of plastic and metallic materials. Engineers at Cambridge Polymer Group have developed an automated optical system that allows real-time assessment of crack length during a fatigue crack test. Two laboratories compared test results using this optical system on UHMWPE samples, with the results presented at the 7th Annual UHMWPE conference in Philadelphia, PA in October 2015. The presentation can be found here.
The third edition of the UHMWPE Biomaterials Handbook was just offered for purchase. This edition contains the history of ultra high molecular weight polyethylene and its use in hip and knee arthroplasty. The new edition contains multiple chapters addressing analytical testing techniques to characterize UHMWPE, wear testing, accelerated aging, antioxidant effects, and advances in UHMWPE processing and formulation development. CPG researchers Braithwaite, Kozak, and Spiegelberg contributed a chapter on characterization techniques on UHMWPE, including details on fatigue crack propagation testing, true stress-true strain measurements, and electron spin resonance spectroscopy.
BE: Please provide a brief overview of Cambridge Polymer Group and the services you provide.
SS: We like to think of ourselves as a one-stop resource for our clients, working everywhere in the product lifecycle from concept through launch and (hopefully not) root-cause analysis.
We are a well-established contract research laboratory that has been operating since the mid-1990’s specializing in polymer science. Our scientists are experienced in analytical testing, polymer chemistry, and product development, testing and analysis. We often serve as either an external routine analytical testing laboratory, or an external research and development facility for our clients.
BE: What does rheological testing involve? SS: Rheology is the study of the flow of matter. Most people are familiar with the concept of viscosity, and how it relates to how easy it is to pour or spread liquids. Viscosity is one of the parameters that comes out of rheological characterization, but we do much more than that.
We can determine the viscoelastic nature of material, which tells you how the material will respond to different rates of deformation, which is important in polymer processing and end use. We can also (almost uniquely) characterize the response of fluids to extensional deformation, such as found in fibre spinning, coating or injection molding.
BE: What type of materials can you test? SS: Polymers are, of course, our main source of testing, but the word ‘polymer’ extends beyond standard synthetic polymers. We do a lot of testing of natural polymers, such as collagen and hyaluronic acid, as well degradable polymers.
These polymers can be on their own, or as blends or composites, or functionally part of a larger device, so you can see that the scope of devices and products that “polymers” covers is far broader than the image that “plastics” alone might conjure up.
In the medical field, we also do a fair amount of testing on the cleanliness of devices, which can include both polymeric and metallic devices. In particular, in rheological testing we can of course test the melt-flow properties of the base resins, but we also have extensive experience in understanding and testing the solution and blend properties of these high molecular weight materials.
The rich and varied response of polymers in solution makes for challenging rheological testing, and understanding the end-use and requirements of the test is critical to get useful results.
A Workshop on Reprocessing of Re-usable Medical Devices will be held Tuesday, November 15, 2016. Sponsored by ASTM Committee F04 on Medical and Surgical Materials and, the workshop will be held at the Renaissance Orlando at SeaWorld in Orlando, FL, in conjunction with the November standards development meetings of the committee. Objectives:
A recent article in Medical Processing Outsourcing (June 2, 2015) estimates that reprocessed medical devices will grow by 19% annually to reach $2.58 billion in 2020. A key element of this successful growth is assurances of cleanliness and safety standards.
Recently, the FDA released a guidance document on reprocessing of reusable devices (March 12, 2015) and held a public meeting on May 14-15, 2015 to discuss infections associated with the use of duodenscopes.
The workshop is intended to bring thought leaders together on the issues involving cleaning of re-usable medical devices to determine the areas of standardization that ASTM should focus on in the next few years.
Topics to be discussed include the following:
History of reprocessing issues
Review of relevant existing ASTM, ISO, AAMI, and FDA standards/documents
Designing of medical devices for reprocessing
Reprocessing
Reprocessing work instructions
3rd party reprocessors experiences
Manufacturers of reprocessing equipment
Testing for biological residues
Test methods
Test soils
Instrumentation
Sterilization of residual soil
Biocompatibility of residual soil/limits
Discussion of new standards development for ASTM to consider
Please contact CPG researcher and workshop co-chair Stephen Spiegelberg with any questions or to submit an abstract.
More details on the workshop can be found on the ASTM web site.
Cambridge Polymer Group will be exhibiting at the Biomed Device Exposition in Boston on May 6-7th.
Come visit us at booth 1147 to see the new analytical tools, formulation capabilities, and project assistance we can provide. If you would like to visit our lab while you are in town, please contact us at info@campoly.com.
Ultra high molecular weight polyethylene (UHMWPE) is commonly used as a bearing surface in hip, knee, shoulder, and other total joint replacement arthroplasties. Aging of UHMWPE that has been irradiated without additional treatment to stabilize the residual free radicals can result in oxidation followed by chain scissioning. Researchers will usually measure oxidation index to characterize shelf‐life, but this technique does not capture the actual degradation due to oxidation. In this study, gamma sterilized UHMWPE was accelerated aged, and the molecular weights of extractable material were characterized with gel permeation chromatography in an attempt to see if this technique can be used to characterize shelf life of the aged material.
The extraction of the polyethylene material in this study shows that there is a molecular weight difference between the unaged and aged material, with the aged material showing broadening in the molecular weight distribution. This change can be explained by oxidative degradation, which is supported by the oxidation index. The test methodology shows that a larger ratio of solvent to sample is required to ensure extraction without gelation of the extracted material, and that 4 hours is sufficient to extract the larger molecular weight species. The impact of the molecular weight change on in vivo performance, however, cannot be discerned from this test.
